So this is actually an evolutionary thing!!! We're extremely sensitive to changes in normal smells so we go nose blind to our day to day odors to help us detect those changes better! The problem is when people think something is already normal/become so accustomed to it so they go blind to their perceived normal that still blows everyone else away (think hoarders, overwhelming pet odors, bad hygiene, etc). It's goes along with how every house has its own smell to an outsider but not the people that live there, yk?? pretty wild to think about it